Implementing a network infrastructure in a seismic acquisition system

ABSTRACT

A method and apparatus implementing a network infrastructure in a seismic acquisition system are disclosed. The apparatus is a seismic acquisition system, comprising a plurality of seismic data sources ( 120 ) capable of generating data; at least one data collection system ( 140 ) utilizing an open network protocol; and at least one line network ( 300 ) connecting the data sources to the data collection system and utilizing an open network protocol. The line network ( 300 ) includes a plurality of data source nodes ( 130 ) at which a portion of the plurality of seismic data sources are respectively attached to the line network; and a router ( 135 ) for routing data generated by the seismic data sources ( 120 ) to the data collection system ( 140 ) through the data source nodes ( 130 ) in accordance with the open network protocol. The method comprises assigning at least two respective network addresses to each one of a plurality of seismic data sources, a plurality of data source nodes, a plurality of routers, and a data collection system; routing data generated by the data sources through the data source nodes and the routers to the data collection system; correlating the network addresses of the seismic data sources to the physical location of the respective seismic data sources; and correlating the physical locations of the respective seismic data sources to the data generated by the respective seismic data sources.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to seismic surveys, and, moreparticularly, implementing a network infrastructure in a seismicacquisition system.

2. Description of the Related Art

Seismic acquisition systems typically are used in seismic surveys. In aseismic survey, an array of seismic receivers is deployed in a selectedarea. One, and usually more, seismic sources are also deployed. Thesources impart acoustic signals into the ground that are reflected andrefracted by subterranean formations back to the receivers. Thereceivers then transmit data indicative of selected characteristics ofthe reflections to a data collection system. The data collection systemthen collects the data, processes and/or pre-processes it, and,typically, transmits to another location for further processing.

Seismic surveys can be generally categorized as land-based andwater-based (or, “marine”), i.e., by whether they are conducted on landor in the water. Each implicates challenges unique from the other. Forinstance, in a marine survey, the seismic sources are usually towed ator near the surface of the water. The acoustic signals must thereforepropagate through the water before they are imparted into the ground, orsea floor. In contrast, sources in a land-based survey can impart theacoustic signals directly into the ground

However, there are also numerous challenges arising from both thesekinds of surveys. One challenge is to accurately know the physicalposition of the sources when they impart the acoustic signals and of thereceivers when they receive the reflections. Also, a modern seismicacquisition operation requires data to be collected from a large numberof individual units; sources, position sensors, seismic sensors, etc.These units act as data sources in the operation. Usually a number ofseparate data collecting systems are involved in the operation, eachemploying their own infrastructure and method for connecting the datasources to the data collecting systems. These connectivityinfrastructures are optimised to be fit for their particular purpose,and have therefore often wildly differing characteristics and means ofoperation. Introducing a new data source, and/or a new data collectingsystem into the operation requires the introduction of a newconnectivity infrastructure, adding complexity to the total system.Alternatively, an existing infrastructure may be adapted to carry thenew information. However, this will often be a complex task in itself.

The present invention is directed to resolving, or at least reducing,one or all of the problems mentioned above.

SUMMARY OF THE INVENTION

The invention, in its various aspects and embodiments, comprises amethod and apparatus implementing a network infrastructure in a seismicacquisition system. The apparatus is a seismic acquisition system,comprising a plurality of seismic data sources capable of generatingdata; at least one data collection system utilizing an open networkprotocol; and at least one line network connecting the data sources tothe data collection system and utilizing an open network protocol. Theline network includes a plurality of data source nodes at which aportion of the plurality of seismic data sources are respectivelyattached to the line network; and a router for routing data generated bythe seismic data sources to the data collection system through the datasource nodes in accordance with the open network protocol. The methodcomprises assigning at least two respective network addresses to eachone of a plurality of seismic data sources, a plurality of data sourcenodes, a plurality of routers, and a data collection system; routingdata generated by the data sources through the data source nodes and therouters to the data collection system; correlating the network addressesof the seismic data sources to the physical location of the respectiveseismic data sources; and correlating the physical locations of therespective seismic data sources to the data generated by the respectiveseismic data sources.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIG. 1 depicts the conduct of a seismic survey in accordance with oneaspect of the present invention including a recording array connected toa data collection system;

FIG. 2A conceptually depicts a computing system such as may be used inimplementing certain aspects of the present invention-namely, portionsof the data collection system;

FIG. 2B is a block diagram of selected components of the hardware andsoftware architectures of the computing system in FIG. 2A;

FIG. 3 illustrates a single line network, the elemental building blockof the recording array in FIG. 1, connected to the data collectionsystem;

FIG. 4 illustrates one particular implementation of the recording arrayin FIG. 1 in which multiple line networks, such as that illustrated inFIG. 3, are employed to facilitate fault tolerance and spread coverage;

FIG. 5A illustrates timing domains of a synchronization techniqueemployed in one particular implementation of the recording array in FIG.1 in accordance with the Network Time Protocol (“NTP”) of the InternetProtocol (“IP”) suite of protocols;

FIG. 5B illustrates a synchronization technique alternative to that inFIG. 5A;

FIG. 6 depicts one embodiment of a method for use in a seismic survey inaccordance with the present invention; and

FIG. 7A and FIG. 7B illustrate the use of the present invention in aland-based seismic survey in one particular embodiment

While the invention is susceptible to various modifications andalternative forms, the drawings illustrate specific embodiments hereindescribed in detail by way of example. It should be understood, however,that the description herein of specific embodiments is not intended tolimit the invention to the particular forms disclosed, but on thecontrary, the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the invention asdefined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a developmenteffort, even if complex and time-consuming, would be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

FIG. 1 depicts the conduct of a seismic survey system 100 in accordancewith one aspect of the present invention. The seismic survey system 100is a land-based survey system. The seismic survey system 100,accordingly, includes a recording truck 105 connected to a seismic array110, which is a recording array in the illustrated embodiment. Therecording array 110 includes a plurality of seismic data sources 120,such as, for example, seismic sources (e.g., vibrators, explosivecharges), positioning sensors (Global Positioning System (“GPS”)sensors), seismic receivers (geophones), etc., on a plurality of lines125. More typically, however, seismic sources, e.g., the seismic source115, are not a part of the recording array 110. The recording array 110also includes a plurality of nodes 130 and at least one router 135,whose function will be discussed further below.

The seismic survey system 100 includes at least one data collectionsystem 140. Note that some alternative embodiments may employ multipledata collection systems 140. The recording truck 105 is equipped with arack-mounted computing apparatus 200, illustrated in FIG. 2A and FIG.2B, with which at least a portion of data collection system 140 isimplemented. The computing apparatus 200 includes a processor 205communicating with some storage 210 over a bus system 215. The storage210 may include a hard disk and/or random access memory (“RAM”) and/orremovable storage such as a floppy magnetic disk 217 and an optical disk220. The storage 210 is encoded with a data structure 225 storing thedata set acquired as discussed above, an operating system 230, userinterface software 235, and an application 265. The user interfacesoftware 235, in conjunction with a display 240, implements a userinterface 245. The user interface 245 may include peripheral 10 devicessuch as a key pad or keyboard 250, a mouse 255, or a joystick 260. Theprocessor 205 runs under the control of the operating system 230, whichmay be practically any operating system known to the art.

The application 265 is invoked by the operating system 230 upon powerup, reset, or both, depending on the implementation of the operatingsystem 230, to administer an open network protocol on the recordingarray 110. The administration of this open network protocol imposes anetwork infrastructure on the seismic acquisition system 100 with whichthe seismic survey is being conducted. A network, in a general sense, isa plurality of functionally interconnected computing systems. Note thata computing system may be as simple as a single computing device (e.g.,a controller or processor) or as complex as many individual computers. Anetwork protocol (or, more simply, a “protocol”) is an agreed uponformat for transmitting information between computing devices. Aprotocol typically specifies transmission characteristics such as errorchecking, data compression, end of message indicators, and returnreceipts. Practically any open network protocol may be employed, but oneparticular implementation employs, e.g., the Internet Protocol (“IP”)suite. “Open” standards are simply standards promulgated by industrygroups that are available to the public. The IP protocol suite, inparticular, specifies a format for “packets,” or datagrams, that may beaddressed to a recipient and then dropped into the network for delivery.

Thus, in the illustrated embodiment, a single IP-based network (i.e.,the recording array 110, data collection system 140) is deployed betweenthe different data sources 120 and data collection system(s) 140,allowing communication between data sources 120 and data collectionsystem(s) 140 over any protocol supported on top of IP, which includesmost modern, open protocols. In addition, the node-to-node nature ofsuch a spread network allows communication between the plurality of datasources 120 and, separately, between the plurality of data collectionsystem(s) 140, thereby opening a broad range of possible applications.Several features of the IP protocol suite are particularly useful asapplied to the seismic acquisition scenario. The generic and wide-spreadnature of IP simplifies adapting new services and applications to theseismic acquisition system. The protocols comprising the IP protocolsuite support dynamically update routing information, which is importantin supporting fault tolerance and high availability.

FIG. 3 illustrates a single line network 300, the elemental buildingblock of the recording array 110 in FIG. 1, connected to the datacollection system 140. The line network 300 comprises a single router135 connected between the data collection system 140 and a plurality ofnodes 130. The nodes 130 are connected to the line 125. Each node 130is, in turn, connected to a string 305 of data sources 120. The datasources 120 may be any mix and match of the typical types of equipmentused in seismic surveys, e.g., sources, position sensors, seismicsensors, etc. Each of the data collection system 140, the router 135,the nodes 130, and the data sources 120 is assigned a unique, networkaddress in accordance with the network protocol administered by the datacollection system 140.

The data source nodes 130 themselves are connected by means of amedium-bandwidth, IP-based network. The data source nodes 130 willtypically be intelligent units, capable of both initiating andparticipating in communications sessions with other data source nodes130 and with the data collection system(s) 140. The data source nodes130 are connected in-line, each data source node 130 connected to atmost two neighbouring data source nodes 130 in the illustratedembodiment. A number of data source nodes 130 will typically beconnected together, forming a string of data source nodes 130, as willbe discussed further below. Terminating such a string will be a networkrouter 135. The router 135 is a computing device that connects multiple,relatively small networks—such as the line network 300—together.Multiple line networks 300, other routers 135, or data collectionsystems 140 may be connected to a single router 135.

The seismic data sources 120 package data into packets (not shown), eachof which contains not only data, but a variety of other information.Some of this information is in what is known as the “header” of thepacket. The header typically contains the network address of thedestination for the packet, e.g., the data collection system(s) 140. Therouter 135 uses this information in the headers of the packets from theseismic data sources 120 and a lookup table (not shown) stored on router135 to determine the packet's destination. The router 135 thencommunicates with other routers 135 to determine the best path to thatdestination through the larger network as a whole. In the illustratedembodiment, the routers 135 communicate among each other using a secondopen protocol called Open Shortest Pass First (“OSPF”), althoughalternatives might include Internet Control Message Protocol (“ICMP”),which is a well known extension to the IP protocol suite. Still otheropen protocols may be used in alternative embodiments. Thus, the router135 behaves in the illustrated embodiment as a standard IP networkrouter, routing traffic to and from the data source nodes 120 on theline networks 300 connected to the router 135, as well as traffic to andfrom the other routers 135 connected to it.

The connections among the seismic data sensors 120, seismic source nodes130, the router 135, and the data collection system 140 are all designedto accommodate the amount of network traffic expected to be travellingthereon. The line 125 implements, in the illustrated embodiment, amedium-bandwidth data path. The connection 310 is a high-bandwidth datapath, sometimes referred to in networking parlance as the “backbone.” Inthe illustrated embodiment, the connection 310 and the line 125 are bothelectrical, and may be implemented using any suitable electricaltechnology known to the art. For instance, twisted wire pairs andshielded coaxial cables might be employed in various embodiments.However, this is not required for the practice of the invention. Theconnection 310 and line 125 may alternatively be optical fibres, forinstance, or a wireless system.

The precise parameters regarding the bandwidth of the line 125 andconnection 310 will be implementation specific, depending on the numberof components (e.g., seismic data sources 120, data source nodes 130,routers 135, and data collection systems 140), the particular protocolimplemented, and the structure of the recording array 110. However,those in the art having the benefit of this disclosure will be able toreadily determine these parameters based on standard networkingprinciples and the specifications of the applicable protocols.Furthermore, whether the line 125 or the connection 310 is “high”bandwidth or “medium” bandwidth is not material to the practice of theinvention so long as they have the capacity to handle the trafficthereon for the given implementation.

Although the line network 300 of FIG. 3 can be used in isolation toconduct a survey, a recording array (e.g., the recording array 110 inFIG. 1) will typically comprise several line networks 300. FIG. 4illustrates one particular implementation 400 of the recording array 110in FIG. 1 in which multiple line networks, such as the line network 300in FIG. 3, are employed to facilitate fault tolerance and spreadcoverage. The degree of fault tolerance and/or spread coverage will behighly implementation specific, depending on the number and arrangementof the line networks 300 therein. Note, however, that variousalternative embodiments may employ the invention without necessarilyusing this “modular” approach.

More particularly, the survey apparatus 400 includes multiple datacollection units 140 (i.e., DC₀-DC₃), multiple routers 135 (i.e.,R₀-R₁₁), multiple data source nodes 130 (i.e., N₀-N₁₅), and multipleseismic data sources 120 (i.e., S₀-S₃₁). Note that the precise numbersof the different types of components is not material to the practice ofthe invention, nor are the ratios. For instance, an alternativeembodiment might employ only a single data collection unit for the samenumber of routers, data source nodes, and seismic data sources. Theprecise numbers of the various pieces of equipment will beimplementation specific. Note that, although not necessarily required topractice the invention, each router 135 is connected to a datacollection system 140 by a backbone 310.

In the embodiment of FIG. 4, a break in more than one line or backbonewill be survivable as long as more than one backbone and line areavailable, and they do not affect the same line; not all backbones arebroken at the same link ‘latitude’; and not all lines are broken. Forinstance:

-   -   a break between the router R₃ and the data source node N₄ and a        break between the data source node N₅ and the router R₄ (i.e.,        in the same link “latitude”) will drop the data source nodes 130        (e.g., N₄, N₅) and the associated seismic data sources 120        (e.g., S₈-S₁₁) from the survey; and    -   a break in the backbone 310 between the routers R₃, R₆, in the        backbone 310 between the routers R₄, R₇, and in the backbone        between the routers R₅, R₈ will drop all components “below” the        routers R₃-R₅ from the survey.        In general, however, the survey apparatus 400 exhibits        relatively high fault tolerance. Furthermore, combinations of        line and backbone network link failures may be survivable        depending on the exact locations of the breaks.

Additional data collection systems 140 can be added to the spreadnetwork at any router 135. There may be more than one data collectionsystem 140 connected, and the data collection systems 140 (e.g., DC₂,DC₃) may be connected at separate routers 135. The data collectionsystems 140 (e.g., DC₁, DC₂, DC₃) serve as local data collection pointscollecting data off a respective backbone that they then forward to adesignated, central collection data system 140 (e.g., DC₀). The physicalarea that may be covered by a spread network (e.g., the spread network400) will be limited by the distance limitations of the networkhardware. In addition, it may be limited by the maximum bandwidth of theline network The routers 135 may be connected to more than one linenetwork (e.g., R₁, R₄, R₇, R₁₀), thus it will be possible to extend thespread network beyond the limitations of one line network by addingmultiple line networks in the in-line direction. To utilize such atopology one might either add multiple high bandwidth network links toone data collection system 140 as in FIG. 1, or add multiple, parallel,data collection systems 140 that collect data from separate parts of thespread network as in FIG. 4.

Another advantage of the spread network of the present invention is thatdynamic muting and load balancing techniques can be used to determinewhich data collection system 140 a given seismic data source 120 shouldcommunicate with. Depending on the configuration and topology of thespread network, different channels, routers 135, or data collectionsystems 140 might receive different levels of traffic. At differenttimes, some routers 135 or data collection systems 140 may be busy whileothers may be idle. Some might even be borderline overwhelmed by thelevel of traffic. The traffic load on various components such as routers135 and data collection systems 140 might also vary over time from verybusy to very idle. For instance, traffic levels may change over time asnew seismic data sources 120 are added, old ones removed, or networkfailures impact the performance of the spread network.

Dynamic routing and load balancing techniques have been developed forcomputing networks to accommodate these types of concerns. Thesetechniques monitor network traffic patterns and adjust network operationto ameliorate the burdens on individual components. These techniques canbe applied to the spread network of the present invention to help ordertraffic therein, adapt to unforeseen exigencies such as equipmentfailures. Dynamic routing and auto configuration of the network willalso facilitate varying the layout and topology of the spread network.This will be particularly useful in “rolling” the spread during seismicoperations.

The open standard-based IP network of the illustrated embodiment isextended with three features adapted to the seismic acquisitionenvironment. One is a synchronization service allowing different datasource nodes 130 on the spread network (e.g., 100 or 400) to havereal-time clocks that are closely synchronized. Seismic surveying, ingeneral, employ tighter synchronization than do the computing networksfor which the open-protocols have been developed. Hence, the use of thesynchronization service. The second is a location mapping serviceenabling the spread network to easily convert a network address to alogical location and vice versa. Seismic surveying also “peg maps” thelogical location of the seismic data sources 120 to their location inthe network. Thirdly, the spread network will support auto-configurationof the network infrastructure itself, e.g. not only will it be possibleto dynamically add and remove clients (end-points) from the activenetwork, but also routers. This is useful not only when performingmaintenance and repair of malfunctioning components, but also when‘rolling’ the seismic spread during normal seismic surveying operations.

Turning first to the synchronization service, FIG. 5A illustrates timingdomains employed in one particular implementation of the recording array110 in FIG. 1. This particular embodiment employs the Network TimeProtocol (“NTP”) of the Internet Protocol (“IP”) suite of protocols. NTPassures accurate synchronization to the millisecond of computer clocktimes in a network of computers. In a standard networking application,NTP synchronizes client workstation clocks to the U.S. Naval ObservatoryMaster Clocks in Washington, D.C. and Colorado Springs, Colo. Running asa continuous background client program on a computer, NTP sends periodictime requests to servers, obtaining server time stamps and using them toadjust the client's clock. The present invention employs NIP in the samefashion.

The IP protocol NTP is extended with propagation delay measurement toprovide sub microsecond accuracy. One data collection system 140 isassigned to be the active synchronization master at any one time. Theactive synchronization master is referred to as “Stratum 1” in NTPparlance. Synch masters will have access to an external accurate timesource (e.g., a Global Positioning System, or “GPS,” receiver) referredto as “Stratum 0.” Alternate synch masters can be defined, and they canuse the mechanism for time distribution described below to verify theintegrity of their respective time sources.

More particularly, the underlying network implementation suppliesaccurate time distribution and clock synchronization features. Theseprimitives are used to recursively distribute the real-time as suppliedby an “active synchronization master.” First, the primitives transmittediteratively from the active synchronization master (stratum 1) to therouter on the backbone connected to the master. This router will then bea backbone network synch master (stratum 2) and will synchronize allrouters on the backbone (stratum 3). Subsequently, each router willsynchronize all line nodes connected to it (stratum 3 or 4). Only thebackbone to which the synch master of the moment is connected will besynchronized directly from the active synchronization master. Otherbackbone networks will have their own network synch masters. Thesenetwork synch masters will take synch from the line network connectingthem to the higher-level stratum. Data collection systems connected tothe spread network can be configured to be synchronization clients,e.g., they can be accurately synchronized with the line nodes, and withother data collection systems without having their own time referencesystems.

Returning now to FIG. 5A, the spread network 500 comprises multiple datacollections systems DC, routers R, data source nodes N, and seismic datasources S as discussed above. The spread network 500 also includes a GPSreceiver 502 that provides a clock CLK for the spread network 500. Thespread network 500 comprises a plurality of synchronization strata 504defined as described above in accordance with the NTP IP protocol. Thestrata 504 are designated STRATUM₀-STRATUM₅. The GPS receiver 502 isSTRATUM₀. The data collection system 506, connected to the GPS receiver502, is the designated synchronization master and constitutes STRATUM₁.The data collection system 508 and router 510, connected between thedata collection system 506 and the rest of the spread network 500,constitutes STRATUM₂. The line network 512 of the routers 514, 516, 518are connected between STRATUM₂ and the rest of the spread 500. Theyconsequently constitute STRATUM₃. Similarly, the line networks 520, 522,524 of the routers 514, 516, 518, respectively, constitute STRATUM₄. Therouters 526, 528, 530 are also a part of STRATUM₄. Finally, the linenetworks 532 and 534 of the routers 528, 530, respectively, and therouters 536, 538 constitute STRATUM₅.

The synchronization begins as the data collection system 506, acting asthe active synchronization master, passing the primitives to STRATUM₂.The data collection system 508 and router 510 are then synchronized tothe clock of the data collection system 506. The router 510 then assumesthe role of “backbone network synch master” for the backbone 540 and therouters 516 and 518 on the backbone 540. The router 510 is also thesynch master for the router 514 on the line network 512. As mentionedabove, each router R synchronizes the lines nodes, including both datasource nodes N and routers R, on the lines to which it is connected.

Thus, the router 510 passes the primitives to each of the routers 514,516, 518 in STRATUM₃. Each of the routers 514, 516, 518, in turn, thenpasses the primitives to the line nodes on the lines connected thereto.The router 514 therefore passes the primitives to the nodes N androuters R on the line network 520, the router 516 does the same on theline network 522, and the router 518 for the line network 524. Thus, therouters 526, 528, 530 in STRATUM₄ are synched to the routers 514, 516,518, respectively, in STRATUM₃. The routers 528, 530 then pass theprimitives to the routers 536, 538, respectively, in STRATUM₅. Ifadditional line networks and/or routers and/or data collection systemsare added, they can be synchronized to the rest of the spread network500 in the same iterative fashion across additional strata defined inaccordance with the NIP protocol.

It can be shown that the synchronization error of this approach isproportional to √{square root over (n_(hops))} where n_(hops) is thenumber of discrete network link hops from stratum 0. As will beappreciated by those skilled in the art having the benefit of thisdisclosure, a “network link hop” occurs with the regeneration of networktime stamps using local real-time clocks. Thus, in the embodiment ofFIG. 5A, there is a “network link hop” between each of the strataSTRATUM₀-STRATUM₅. The hierarchical scheme imposed by the NTP protocolkeeps n_(hops) small relative to the total size of the spread network500. Note that alternate routing for synchronization is possible usingexactly the same fail over and rerouting protocols as for data traffic.That is, in FIG. 5A, a node N (e.g., the node 542) will by default besynchronized by a router R (e.g., the router 514). But, another router R(e.g., the router 510) is also available and able to supplysynchronization to the node N, albeit in a higher stratum. The abilityto supply synchronization along multiple paths also allows time andsynchronization verification in the spread network 500. This may bedone, e.g., by comparing multiple synchronization sources against eachother.

An alternative synchronization technique is illustrated in FIG. 5B. Theunderlying principle of this spread synchronization technique is “localReal Time Clock” (“RTC”) adjustment using:

-   -   timestamps, corresponding to uniquely identifiable transmission        events, distributed by one or more synchronization masters;    -   RTC sampling by synchronization slaves triggered by the        corresponding reception events;    -   deterministic propagation delay separating transmission and        reception events; and    -   measurement of this propagation delay.        The local RTC error is assumed to be the difference between the        locally measured reception time and (timestamp+propagation        delay). The illustrated embodiment assumes that the transmission        event used for synchronization is the moment at which the first        bit of the frame containing a timestamp is clocked onto the        line.

RTC synchronization with (sub) micro second accuracy is desirable forseismic acquisition. This level of accuracy generally cannot be achievedif propagation delays, timestamp generation and RTC sampling are notsufficiently deterministic, as is the case with NTP. Fault tolerance andauto configurability generally cannot be achieved if timestamps aredistributed by a single source along fixed routes whose delays aremeasured during system boot. Similarly, bit synchronous networks, wherelocal transmission clocks are derived from those recovered from incomingsignals, couple spread synchronization to the initial spread topology.

The primary techniques for decoupling spread synchronization from globaltopology in the illustrated embodiment are:

-   -   regenerating timestamps throughout the spread using local RTCs;    -   controlling local transmission clock signals locally; and    -   measuring propagation delays only from the nearest points of        regeneration.        In order to give maximum flexibility and minimum inter-node        dependence, each node in the spread will generate timestamps        using its RTC. Frames containing timestamps will also include        values indicating the number of hops from, and the stratum value        (e.g. clock quality) of, the spread synchronization master.        These additional values will be used to auto configure a        master-slave hierarchy with respect to clock adjustments,        assuring that all RTCs in the spread converge towards that of        the spread sync master. Each node in the spread—except the        spread sync master—slaves itself to the neighbour providing the        best acceptable timing information. Until timing information of        an acceptable stratum becomes available, nodes remain        unsynchronised.

FIG. 5B illustrates the flow of timing information in a fragment 550 ofa spread having two backbones 552, 554 connected to the samesynchronization master 556. The synchronization master 556 may be, forinstance, a data collection system with access to a GPS receiver toprovide a clock in the manner of the data collection system 506 and GPSreceiver 502 in the embodiment of FIG. 5A. Returning to FIG. 5B, notethat each of the synchronization master 556, and slaves 558, 560, 562,564, 566 each have a RTC 568. Note that each of the slaves 562, 564, 566are slaved to the RTC 568 of their neighbour, i.e., the slaves 558, 562,and 564, respectively. The slaves 562, 564, 566 may be seismic datasources, data source nodes, routers, or data collection systems. Theslaves 558, 560 are slaved to their neighbours, the slave 558 and thesynchronization master 556, respectively. The slaves 558, 560, in theillustrated embodiment, are routers.

Each point of timestamp regeneration introduces a potential new sourceof clock drift and jitter. However, basic statistical principles dictatethat in the absence of systematic errors the expected accumulated clockerror grows only as the square root of the number regeneration pointstraversed, i.e., √{square root over (n_(hops))}. Note that this is thesame as for the embodiment of FIG. 5A. In the illustrated embodiment,there are no hops to the synchronization master 556, there is one hop tothe slaves 558, 566, and there are two hops to the slaves 552, 562, and564.

This “domino synchronization” scheme illustrated in FIG. 5B onlymeasures propagation delay between immediate neighbours, as thetimestamps used by a node to adjust its RTC will be generated by one ofits neighbours. Because nodes synchronize themselves using onlyinformation from their immediate neighbours, the spread topology canchange without seriously disrupting spread synchronization. The basicelements of the scheme are thus:

-   -   auto configuration of the (nearest neighbour) master-slave        hierarchy,    -   regular propagation delay measurements between immediate        neighbours; and    -   RTC adjustments.        Note that this scheme provides fail over as for data traffic.        More particularly, if the link between a node and the neighbour        acting as its synchronization master fails, the node can switch        to any other neighbour providing acceptable timing information.        Note further that data collection systems connected to the        spread network can be configured to be synchronization clients,        e.g. they can be accurately synchronized with the line nodes,        and with other data collection systems without having their own        time reference systems.

Turning now to the location mapping service, the order and orientations(e.g., 180° rotations) of data source nodes N are determined to perform“peg mapping.” That is, this information is determined to generate amapping between seismic survey topology (e.g., lines and receiverpoints) and network topology. The peg mapping is performed because theabsence of true geographical positioning information for data sourcenodes N and their seismic data sources S. Peg mapping is not typically apart of open networking standards, although it is performed inconventional, proprietary protocols. Therefore an additionalprotocol—mapping node order, node orientation, and defining topologyevents—is used in conjunction with the open protocol. Topology eventsinclude: link up, link down (or node failure) plus node address change.Local location information is collected by the routers R and madeavailable, as a service, to interested applications. Peg mappingtechniques used on conventional proprietary networks may be employed forthis purpose.

Finally, auto configuration of the network infrastructure simplifiesflexible deployment and helps automate reconfiguration, e.g., for spreadroll and line fault recovery. The core of the auto configuration schemeemployed in this particular embodiment is hierarchical addressingcoupled with a hierarchy of configurable configuration servers that usecontention to resolve conflicts. Note, however, that alternativeaddressing and contention approaches may be used in alternativeembodiments.

Network addresses in the illustrated embodiment consist of a networknumber part and a node part in accordance with the open protocol appliedas discussed above. Network numbers at a particular level in thehierarchy are generated by combining network and nodes numbers from thenext higher level using what is basically a left shift (or promotion) ofthe node part. This addressing may be performed in conventional fashion.

The illustrated embodiment couples this hierarchical addressing with ahierarchy of configurable “configuration servers.” The configurationservers also operate in a hierarchical fashion. Three levels ofconfiguration servers are defined in the illustrated embodiment:

-   -   a unique root server (with zero or more backup servers for        redundancy), which allocates backbone numbers;    -   backbone servers, one per backbone, which allocate backbone        addresses having a network part based on backbone number, and    -   line network servers, one per line network, which allocate line        network addresses having a network part based on router        backbone-port addresses.        Note that, in alternative embodiments, different levels may be        employed in addition to, or in lieu of, those listed above.

For instance, referring now to FIG. 4, assume the data collection unitDC₁, has been designated as the unique root server. The data collectionunit DC₁ configures itself and passes configuration information to thebackbone servers. In the illustrated embodiment, the backbone serverswould be the routers R₀, R₁, and R₂. The backbone routers configurethemselves and then pass configuration information on to the linenetwork servers. For example, the routers R₁, R₂, R₄, R₅, R₇, R₈, R₁₀,and R₁₁ may be line network servers. The line network servers thenconfigure themselves. Note that the redundancy of the configuration inFIG. 4 provides an alternative configuration, as well. For instance, thedata collection unit DC₂ may be the unique root server, the routers R₂,R₅, R₈, and R₁₁ may be the backbone servers, and the routers R₀, R₁, R₃,R₄, R₆, R₇, R₉, and R₁₀ may be the line network servers.

Conflicts between two peer-level configuration servers (i.e., root vs.root, backbone vs. backbone, or line network vs. line network) areresolved through contention. In the illustrated embodiment, the greaterof two unique numerical box identifiers wins. Consider, for instance, ascenario in which both the data collection unit DC, and the datacollection unit DC₂ have both inadvertently been designated as the rootserver. This would be undesirable because they might assign the sameaddresses to different backbone routers or different addresses to thesame backbone router. Once the data collection units DC₁, DC₂ becomeaware of the conflict, they resolve the contention by comparing theunique identifiers. The data collection unit 140 having the lowestunique identifier backs off, and the other proceeds with theauto-configuration.

The unique identifiers can either be box serial numbers or some otherunique identifier having the same format but which has been set bysoftware. The source of the unique identifier is not material to thepractice of the invention so long as each potential server's identifieris unique relative to the others. Note that the network addresses do notnecessarily have anything to do with the unique identifiers used forresolving contention. The ability to set an arbitrary value by softwarecan be used by a data collection system wishing to prevent completereconfiguration of the spread as new nodes are added.

A configuration server keeps track of its immediate children. When, andif, a configuration server loses contention, it notifies its immediatechildren that they must restart before it terminates its services. Therestarted children thus obtain new configuration information from thewinning server. When a child server is asked to restart, it sendsfurther notification to its children before doing so. In order tofacilitate node tracking when contention results in reconfiguration, thelocation services will be notified, so that address updates can bepublished to interested applications.

Thus, in operation, and as shown in FIG. 6, a respective network addressis assigned (at 605) to each one of the seismic data sources, datasources data source nodes, routers, and data collection systems.Typically, this is performed by the line or backbone server 135 (R₀, R₁,or R₂₀), although this is not necessary to the practice of theinvention. Should two different pieces of equipment attempt to assignaddresses, the conflict is, in the illustrated embodiment, resolvedthrough contention as described above. The addresses are assigned (at605) each time the network infrastructure is configured. Thus, theaddresses may be assigned (at 605) either upon power-up as the recordingarray is deployed, or upon reset, i.e., when the network infrastructureis automatically reconfigured for, e.g., a link going down or coming up.

Once the network infrastructure is up and running, with addressesassigned (at 605), data generated by the data sources is routed (at 610)through the data source nodes and the routers to a data collectionsystem. The manner in which the data is packaged by the seismic datasources and routed will be implementation specific, depending on theparticular open protocol in use. Again, the illustrated embodimentemploys the IP protocol as its open protocol, but others may be used inalternative embodiments. Operation of the network infrastructure issynchronized as was described above using, in the illustratedembodiment, the NTP protocol.

The collected data is then processed. The processing involves firstcorrelating the network addresses of the seismic data sources to thelogical location of the respective seismic data sources (at 615). Thisinvolves first peg mapping the network addresses of the seismic datasources to their logical location in the recording array, as wasdiscussed above. Next, the logical locations of the respective seismicdata sources to the data generated by the respective seismic datasources is correlated (at 620). Ordinarily, the data is transmitted fromthe seismic data sources to the data collection system in packets. Eachpacket typically includes not only data, but a header that includesinformation such as the source and destination network addresses of thepacket. Thus, the source network address can be extracted from theheader of the packet and, having already been correlated to the logicallocation (at 615), the logical location can then readily be correlatedto the data (at 620).

FIG. 7A and FIG. 7B illustrate the use of the present invention in aland-based seismic survey. FIG. 7A shows the seismic recording array110, first shown in FIG. 1, connected to the recording truck 105. Theseismic source 115 is also shown. The data collection system 140 isshown centrally located on the recording truck 105. However, as will beappreciated by those skilled in the art, various portions of the datacollection system 140 may be distributed, e.g., across the recordingarray 110, in alternative embodiments.

Once the recording array 110 is assembled and deployed, a networkaddress is assigned (at 710, FIG. 7B) in accordance with an open networkprotocol to each one of a plurality of seismic data sources 120, datasource nodes 130, and routers 135 (all shown in FIG. 1). The seismicsource 115 generates a plurality of seismic survey signals 715 (at 718,in FIG. 7B) in accordance with conventional practice. The seismic surveysignals 715 propagate and are reflected by the subterranean geologicalformation 725. The seismic data sources 120 receive (at 730, FIG. 7B)the reflected signals 735 of the generated signals 715. Note that,although not shown, some of the seismic data sources 120 are alsoreceiving positioning signals, e.g., GPS signals, in accordance withconventional practice.

The seismic data sources 120 then generate (at 738, in FIG. 7B) datarepresentative of the reflections 735. In the illustrated embodiment,the seismic data sources 120 receiving positioning signals also generatedata representative of the received positioning signals. The generateddata is then routed (at 740, in FIG. 7B) from the seismic data sources120 through the data source nodes 130 and the routers 135 to the datacollection system 140 in accordance with the open network protocol. Thedata collection system 140 collects the data for processing. The datacollection system 140 may process the data itself, store the data forprocessing at a later time, or transmit the data to a remote locationfor processing.

In the illustrated embodiment, the data collection system 140 processesthe data itself. The data collection system 140 correlates the networkaddresses (at 745, in FIG. 7B) of the seismic data sources 120 to thephysical location of the respective seismic data sources 120. Thisinvolves first determining the logical location of the network addressin the recording array 110 using the peg mapping service as wasdescribed above. The actual position of the logical location is thendetermined. The determination of the actual position may be performedusing any technique known to the art suitable to the seismic datasources being implemented and the data they generate. The physicallocations of the respective seismic data sources 120 are then correlated(at 750, in FIG. 7B) to the data generated by the respective seismicdata sources 120. The data is then used to develop (at 755, in FIG. 7B)a representation of the subterranean formation 725 from the data.

Some portions of the detailed descriptions herein are presented in termsof a software implemented process involving symbolic representations ofoperations on data bits within a memory in a computing system or acomputing device. These descriptions and representations are the meansused by those in the art to most effectively convey the substance oftheir work to others skilled in the art. The process and operationrequire physical manipulations of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical, magnetic,or optical signals capable of being stored, transferred, combined,compared, and otherwise manipulated. It has proven convenient at times,principally for reasons of common usage, to refer to these signals asbits, values, elements, symbols, characters, terms, numbers, or thelike.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantifies. Unlessspecifically stated or otherwise as may be apparent, throughout thepresent disclosure, these descriptions refer to the action and processesof an electronic device, that manipulates and transforms datarepresented as physical (electronic, magnetic, or optical) quantitieswithin some electronic device's storage into other data similarlyrepresented as physical quantities within the storage, or intransmission or display devices. Exemplary of the terms denoting such adescription are, without limitation, the terms “processing,”“computing,” “calculating,” “determining,” “displaying,” and the like.

Note also that the software implemented aspects of the invention aretypically encoded on some form of program storage medium or implementedover some type of transmission medium. The program storage medium may bemagnetic (e.g., a floppy disk or a hard drive) or optical (e.g., acompact disk read only memory, or “CD ROM”), and may be read only orrandom access. Similarly, the transmission medium may be twisted wirepairs, coaxial cable, optical fibre, or some other suitable transmissionmedium known to the art. The invention is not limited by these aspectsof any given implementation.

This concludes the detailed description. The particular embodimentsdisclosed above are illustrative only, as the invention may be modifiedand practiced in different but equivalent manners apparent to thoseskilled in the art having the benefit of the teachings herein.Furthermore, no limitations are intended to the details of constructionor design herein shown, other than as described in the claims below. Forinstance, although the illustrated embodiment employs the invention inthe context of a land-based survey, alternative embodiments mayimplement the invention seabed acquisition. In this alternativeembodiment, the seismic data sources might include seismic sources suchas a vibrator or an explosive charge, seismic receivers such asgeophones, and positioning instruments such as GPS receivers. It istherefore evident that the particular embodiments disclosed above may bealtered or modified and all such variations are considered within thescope and spirit of the invention. Accordingly, the protection soughtherein is as set forth in the claims below.

1. A seismic acquisition system, comprising: a plurality of seismic datasources capable of generating data; at least one data collection systemutilizing an open network protocol; and at least one line networkconnecting the data sources to the data collection system and utilizingan open network protocol, the line network including: a plurality ofdata source nodes at which a portion of the plurality of seismic datasources are respectively attached to the line network; and a router forrouting data generated by the seismic data sources to the datacollection system through the data source nodes in accordance with theopen network protocol.
 2. The seismic acquisition system of claim 1,wherein the router routes data to the seismic data sources.
 3. Theseismic acquisition system of claim 1, wherein each of the data sourcenodes is assigned at least two respective network addresses under theopen network protocol.
 4. The seismic acquisition system of claim 1,further comprising at least one additional router for routing datagenerated by the seismic data sources to the data collection systemthrough the data source nodes in accordance with the open networkprotocol.
 5. The seismic acquisition system of claim 1, wherein the datacollection system is assigned at least two respective network addressesunder the open network protocol.
 6. The seismic acquisition system ofclaim 1, wherein the seismic cable comprises a land-based seismic cableor an ocean bottom cable.
 7. The seismic acquisition system of claim 1,wherein the seismic data sources include at least one of seismicsources, seismic receivers, and positioning instruments.
 8. The seismicacquisition system of claim 7, where in the seismic sources include atleast one of an air gun, a vibrator, and an explosive charge.
 9. Theseismic acquisition system of claim 7, wherein the seismic receiversinclude at least one of a hydrophone and a geophone.
 10. The seismicacquisition system of claim 1, wherein the open network protocolincludes the Internet Protocol.
 11. The seismic acquisition system ofclaim 10, further comprising a synchronization service.
 12. The seismicacquisition system of claim 11, wherein the synchronization servicecomprises the Network Time Protocol.
 13. The seismic acquisition systemof claim 1, wherein the at least one data collection system furtheradministers at least one of: a synchronization service synchronizing aplurality of clocks for the data collection system, the router, the datasource nodes, and the seismic data sources; a location mapping servicefor mapping between network addresses and logical locations of the datacollection system, the router, the data source nodes, and the seismicdata sources; and an auto-configuration capability for automaticallyreconfiguring the network upon removal of any one of the router, thedata source nodes, or the seismic data sources, or upon the addition ofan additional piece of seismic equipment.
 14. The seismic acquisitionsystem of claim 13, wherein the synchronization service comprises theNetwork Time Protocol.
 15. The seismic acquisition network of claim 13,wherein the synchronization service tolerates changes in topology. 16.The seismic acquisition system of claim 13, wherein the synchronizationservice synchronizes the clocks hierarchically.
 17. The seismicacquisition network of claim 13, wherein the synchronization servicetolerates breaks in the attachment between at least one seismic datasource and the line network.
 18. The seismic acquisition system of claim13, wherein the location mapping service maps: an order for the datacollection system, the router, the data source nodes, and the seismicdata sources; an orientation for each of the data collection system, therouter, the data source nodes, and the seismic data sources; and aplurality of topology events.
 19. The seismic acquisition system ofclaim 18, wherein the topology events include at least one of a linkgoing up, a link going down, and a node address change.
 20. The seismicacquisition system of claim 13, wherein the at least one data collectionsystem comprises a plurality of data collection systems and thesynchronization service, the location mapping service, and theauto-configuration capability are administered by more than one of theplurality of data collection systems.
 21. A method for use in a seismicsurvey, the method comprising: assigning at least two respective networkaddresses to each one of a plurality of seismic data sources, aplurality of data source nodes, a plurality of routers, and a datacollection system; routing data generated by the data sources throughthe data source nodes and the routers to the data collection system;correlating the network addresses of the seismic data sources to thephysical location of the respective seismic data sources; andcorrelating the physical locations of the respective seismic datasources to the data generated by the respective seismic data sources.22. The method of claim 21, wherein assigning the at least tworespective network addresses to each one of a plurality of seismic datasources includes assigning at least two respective network addresses toeach one of a plurality of seismic data sources including at least oneof a seismic source, a seismic receiver, and a positioning instrument.23. The method of claim 21, further comprising at least one of:synchronizing a plurality of clocks for the data collection system, therouter, the data source nodes, and the seismic data sources; mappingbetween network addresses and logical locations of the data collectionsystem, the router, the data source nodes, and the seismic data sources;and automatically reconfiguring the network upon removal of any one ofthe router, the data source nodes, or the seismic data sources, or uponthe addition of an additional piece of seismic equipment.
 24. The methodof claim 23, wherein synchronizing the plurality of clocks includessynchronizing the clocks hierarchically.
 25. The method of claim 23,wherein mapping between network addresses and logical locations of thedata collection system includes: mapping an order for the datacollection system, the router, the data source nodes, and the seismicdata sources; mapping an orientation for each of the data collectionsystem, the router, the data source nodes, and the seismic data sources;and mapping a plurality of topology events.